Transmission control, function
The function sequence is described in the following steps:
Transmission control, general
Function sequence for basic shift program
Function sequence for electronic and hydraulic transmission control
Function sequence for kickdown
Transmission control, general
The function of the fully integrated transmission control unit consists of the evaluation of various input signals (relevant for the transmission function). Depending on this, the electromechanical hydraulic valves (solenoids) are actuated, which in turn determine the transmission ratio of the automatic transmission (gear selection) and the working pressure.
The solenoids are positioned on the fully integrated transmission control (VGS) electric controller unit. This then realizes the hydraulic functionality.
Function sequence for basic shift program
The basic shift program includes upshift and downshift characteristics for all 9 gears, designed for the following situations:
Empty vehicle
Warm operating condition
Smooth road
Sea level
Slow accelerator release:
Undesired downshifts in the upper vehicle speed range are prevented.
Rapid accelerator release:
Upshifting to next gear is prevented and only permitted again when the vehicle accelerates more slowly.
The shift programs are adapted by offsetting the shift characteristics depending on the following parameters:
Load condition of vehicle
Change in driving resistance
Accelerator pedal movement
The fully integrated transmission control unit monitors and shifts depending on the following parameters:
Vehicle speed
Selected drive range at DIRECT SELECT lever (S16/13)
Accelerator pedal position
Transmission mode selection
Selected gear, for short-term M mode
Signals on the drive CAN
The vehicle speed is calculated using the wheel speed signals. The calculated vehicle speed is sent by the instrument cluster to the fully integrated transmission control unit.
Function sequence for electronic and hydraulic transmission control
While electronic transmission control is responsible for gear selection and adapting pressures to the torque to be transferred, power supply control for the automatic transmission is performed by the hydraulic elements in the fully integrated transmission control (VGS) electric controller unit.
The hydraulic elements (hydrodynamic torque converter, shift elements, hydraulic transmission control) are supplied with oil via an oil pump (primary pump) connected to the drive shaft and/or via the electric auxiliary oil pump (M42).
The transmission control system makes possible a precise adaptation of the pressure to the respective operating states and to the engine output during the gearshift phase, resulting in a significant improvement in shift quality. It is possible to reach the engine rpm limit in the individual gears using full throttle and kickdown.
The shift range can be changed while driving in the forward gears. The transmission control system prevents any impermissible high engine speeds with a downshift lockout device.
Furthermore, the transmission control offers the advantage of flexible adaptation to various vehicle versions.
The electrical auxiliary oil pump ensures the oil supply of the hydraulic system when the combustion engine is switched off. It also supports the primary pump in the combustion engine's lower speed range. The electrical auxiliary oil pump is actuated directly over the fully integrated transmission control unit.
Function sequence for kickdown
The driver's wish for maximum acceleration is met by the kickdown function.
The kickdown function is activated from a pedal travel of > 90 % at the accelerator pedal.
The "kickdown" signal is sent by the ME-SFI control unit (N3/36), which sends the engine management status to the fully integrated transmission control unit via the drive CAN.
Based on this information the fully integrated transmission control unit actuates the solenoid valves so that upshifts and downshifts take place at an increased engine speed in order to achieve maximum performance.
The forced downshift into the next lower gear is performed when transmission temperatures are too high and vehicle speed is too low.
Referenced documents
- gf2710d9992tsa Overview of system components of automatic transmission (AT)